The present invention relates to a flow control device of a helically-shaped intake port for use in a diesel engine.
A helically-shaped intake port normally comprises a helical portion formed around the intake valve of an engine, and a substantially straight inlet passage portion tangentially connected to the helical portion. However, if such a helically-shaped intake port is so formed that a strong swirl motion is created in the combustion chamber of an engine when the engine is operated at a low speed under a light load, that is, when the amount of air fed into the cylinder of the engine is small, since air flowing within the helically-shaped intake port is subjected to a great flow resistance, a problem occurs in that the volumetric efficiency is reduced when the engine is operated at a high speed under a heavy load, that is, when the amount of air to be fed into the cylinder of the engine is large.
In order to eliminate such a problem, the inventor has proposed a flow control device for use in a gasoline engine. In this flow control device, a bypass passage, branched off from the inlet passage portion and connected to the helix terminating portion of the helical portion, is formed in the cylinder head of an engine, and a normally closed type flow control valve, actuated by an actuator, is arranged in the bypass passage and opened under the operation of the actuator when the amount of air to be fed into the cylinder of the engine becomes larger than a predetermined amount. In this flow control device, when the amount of air fed into the cylinder of the engine is large, that is, when the engine is operating under a heavy load at a high speed, a part of the air introduced into the inlet passage portion is fed into the helical portion of the helically-shaped intake port via the bypass passage. This reduces the flow resistance of the helically-shaped intake port, thus, enables high volumetric efficiency. This flow control device, however, is just the embodiment of the basic principle of operation and is constructed so that it is suited for a gasoline engine. Consequently, in order to create a swirl motion, suited for a diesel engine, in the combustion chamber without the trade-off of volumetric efficiency, it is necessary to control the amount of air fed into the helical portion from the bypass passage so that such a control is suited for a diesel engine.